Wetzel, your first job is to create a profile blueprint of the rifle. Start by drawing the barrel, and then add the other parts in full scale.
The commercial breeches that are available often have the wrong profile. The standing breech on a Hawken should begin to bend downward immediately behind the plug. When you do this, you will now have to change the curve of the rest of the tang to match your drawing. Watch for any sideways bending while you are at it. Having fit the tang to the plug, and the plug to the barrel, I solder the two together with soft solder. Then I can turn the barrel up-side-down to see it there is any sideways bending to the tang. I straightened out mine using Ken Guys system with three rods in the vise, to put the pressure where it was needed...worked like a hot @!*%. These tangs can be easily bent cold.
The tang gets soldered to the plug after you've inlet the barrel into your stock...then the whole tang goes in, lined up neatly by the barrel channel. Remember that as you go down, the tang will also go rearward too, a little. With that hour-glass swamp in the tang, this can result in gaps if you are not careful. Available castings have draft cast right into them, so I clean them up with a file and abrasive to finished polish right before I inlet them. You don't want to be taking off metal after the inlet is perfect.
Once you have the barrel and tang successfully inlet, you can congratulate yourself, because the rest of the build is pretty straight forward. I can't think of any other "issues" that might cause problems. But if you have a question, I'll be pleased to try to answer it.
Smylee, I really like those stepped tangs too, and have never inlet one. They'd be similar to inletting the tang on a Southern Mountain rifle, I'm thinking. Again, remember that as you go further down into the wrist, you will also be going toward the butt plate. It may be as much as 1/16" so take that into consideration when you file the draft into the edges of the tang. When inletting use a transfer colour and only cut away that which is on the back edges of the inlet.. Remember that if you took away all of the colour, you would have a gap. Ideally, you want to have solid colour on the inlet when you have it all the way down. Take you time and keep chisels shaving sharp.
Harry, I'm looking forward to trying out this new sight. I filed mine out of a piece of 3/4" square stock. Drill the 3/16" hole first, then the ball mill to recess the front, then hacksaw and file. I'll bring it to Heffley, and we can use it in the sillouette match. I won a 200 yard match with my first Hawken, years ago at Thompson Mt. shooting against the cartridge guys. It was a .62 cal as well.